Repair process

ABSTRACT

In accordance with the present invention, a process for repairing metal workpieces, such as turbine engine components, is provided. The process comprises the steps of forming a braze paste containing a first nickel base alloy material containing boron and chromium and a second nickel base alloy material containing chromium and cobalt, applying the brazing paste to an area of the metal workpiece containing at least one crack, and subjecting the workpiece and the brazing paste to a brazing cycle by heating the brazing paste and the workpiece, preferably to a temperature in the range of from 2000 to 2200 degrees Fahrenheit. During the brazing cycle, the brazing paste flows into and fills the at least one crack and thus repairs the metal workpiece.

BACKGROUND OF THE INVENTION

The present invention relates to a process for repairing cracks in metalworkpieces and more particularly to a brazing paste used in said repairprocess.

Metal workpieces, such as turbine engine components, often encounterdifficult work environments. As a result of the harshness of the workenvironments, cracks may develop in the workpieces over the course oftheir service life.

Over the years, many techniques have been developed to repair the cracksin such metal workpieces. These techniques include welding and brazingthe metal workpieces to repair the cracks. Despite the existence ofthese techniques, there remains a need for more effective repairprocesses and repair products.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide aprocess for repairing cracks in metal workpieces.

It is a further object of the present invention to provide a brazingpaste for use in a process for repairing cracks in metal workpieces.

The foregoing objects are attained by the process and braze paste of thepresent invention.

In accordance with the present invention, a process for repairing metalworkpieces, such as turbine engine components, is provided. The processcomprises the steps of forming a braze paste containing a first nickelbase alloy material containing boron and chromium and a second nickelbase alloy material containing chromium and cobalt, applying the brazingpaste to an area of the metal workpiece containing the cracks, andperforming a brazing cycle by heating the brazing paste and theworkpiece.

Further, in accordance with the present invention, a braze paste for usein the repair of cracks in metal workpieces broadly comprises a firstnickel base alloy material containing boron and chromium and a secondnickel base alloy material containing chromium and cobalt.

Other details of the repair process of the present invention, as well asother objects and advantages attendant thereto, are set forth in thefollowing detailed description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, a process for repairing cracksin a metal workpiece, such as a turbine engine component, is provided.The process broadly comprises forming a braze paste containing a firstnickel base alloy material containing boron and chromium and a secondnickel base alloy material containing chromium and cobalt, applying thebrazing paste to an area of the metal workpiece containing the cracks,and performing a brazing cycle by heating the brazing paste and theworkpiece. The brazing paste preferably contains from 20 wt % to 60 wt %of the first nickel base alloy material and the balance comprising thesecond nickel base alloy material. In a most preferred embodiment, thefirst nickel base alloy material and the second nickel base alloymaterial are present in a ratio of 1:1.

While it is preferred to form the braze paste using the aforementionedproportions of the first and second nickel base alloy materials, thebraze paste can be formed with the second nickel based alloy materialbeing mixed with a quantity of the first nickel based alloy materialsufficient to cause adequate flow during the braze cycle.

In one embodiment of the present invention, the first nickel base alloymaterial preferably contains nickel as a major constituent and from 14wt % to 16 wt % chromium and from 2.4 wt % to 3.0 wt % boron. An exampleof a suitable first nickel base alloy material is one having acomposition consisting of from 14 to 16 wt % chromium, from 2.4 to 3.0wt % boron, up to 0.15 wt % total other elements, and the remaindernickel and inevitable impurities.

The second nickel base alloy material preferably has a compositioncontaining from 45 wt % nickel to 51 wt % nickel, from 22 wt % to 23 wt% chromium, and from 18.5 wt % to 19.5 wt % cobalt. An example of onesuch second nickel base alloy material is a nickel base alloy materialconsisting of from 22.0 wt % to 23.0 wt % chromium, from 18.5 wt % to19.5 wt % cobalt, from 3.5 wt % to 4.0 wt % titanium, from 1.8 wt % to2.2 wt % tungsten, from 1.7 wt % to 2.0 wt % aluminum, from 1.2 wt % to1.5 wt % tantalum, from 0.8 wt % to 1.2 wt % niobium, from 0.13 wt % to0.17 wt % carbon, up to 0.20 wt % manganese, up to 0.015 wt %phosphorous, up to 0.10 wt % copper, up to 0.25 wt % iron, up to 0.10 wt% silicon, up to 0.04 wt % zirconium, from 0.001 wt % to 0.008 wt %boron, up to 0.005 wt % sulfur, up to 0.005 wt % nitrogen, up to 0.003wt % oxygen, up to 0.0005 wt % silver, up to 0.0005 wt % lead, up to0.00005 wt % selenium, up to 0.00003 wt % bismuth, up to 0.00005 wt %tellurium, up to 0.00005 wt % thallium, and the balance nickel andinevitable impurities.

To form the braze paste, the first and second nickel base alloymaterials are provided in powder form. The first and second nickel basealloy materials are then mechanically mixed to form the brazing paste.If desired, the first and second nickel base alloy materials may bemixed with a binder, such as Nicrobraze S binder, to form the brazingpaste. Any suitable mechanical mixing means known in the art may be usedto form the brazing paste.

The braze paste may be applied to an area of the workpiece containingthe cracks using any suitable means known in the art. Prior to applyingthe braze paste, a crack to be filled may be cleaned of any debris usingany suitable means known in the art.

After the braze paste has been applied to the area containing thecrack(s) to be repaired, the braze paste and the workpiece are subjectedto a brazing cycle during which the workpiece and the braze paste areheated to a temperature in the range of from 2000 degrees Fahrenheit to2200 degrees Fahrenheit for a time period sufficient to cause thebrazing paste to flow into and fill the crack(s). Any suitable meansknown in the art may be used to perform the brazing cycle at the abovetemperature range.

In some instances, it may be desirable to prefill the crack(s) with thesecond nickel base alloy material in powder form. This is because duringthe brazing cycle treatment, the first nickel base alloy materialbecomes liquid, while the second nickel base alloy material stays solid.The solid is carried along with the liquid when the mixture flows into acrack to be repaired.

The braze paste used in accordance with the present invention isadvantageous in that it allows the repair of cracked components withoutcausing undesirable metallurgical changes in the repair area or adjacentparent material.

The repair process of the present invention may be used to repair gasturbine engine components, both for flight and power generationapplications.

While the metal workpieces being repaired may be formed from anysuitable substrate material, such as nickel based alloys, the process ofthe present invention works particularly well when the workpiece isformed from the same material as that forming the second nickel basealloy.

It is apparent that there has been provided in accordance with thepresent invention a repair process which fully satisfies the objects,means, and advantages set forth hereinbefore. While the presentinvention has been described in the context of specific embodimentsthereof, other alternatives, modifications, and variations will becomeapparent to those skilled in the art having read the foregoingdescription. Accordingly, it is intended to embrace those alternatives,modifications, and variations as fall within the broad scope of theappended claims.

1. A process for repairing at least one crack in a metal workpiececomprising the steps of: forming a braze paste containing a first nickelbase alloy material containing boron and chromium and a second nickelbase alloy material containing chromium and cobalt; applying saidbrazing paste to an area of said metal workpiece containing said atleast one crack; subjecting said brazing paste and said workpiece to abrazing cycle by heating said brazing paste and said workpiece; andwherein said braze paste forming step comprises mixing a first nickelbase alloy material consisting from 14 wt % to 16 wt % chromium, from2.4 wt % to 3.0 wt % boron, up to 0.15 wt % total other elements, andthe remainder nickel and inevitable impurities and a second nickel basealloy material consisting of from 22 wt % to 23 wt % chromium, from 18.5wt % to 19.5 wt % cobalt, from 3.5 to 4.0 wt % titanium, from 1.8 wt %to 2.2 wt % tungsten, from 1.7 wt % to 2.0 wt % aluminum, from 1.2 wt %to 1.5 wt % tantalum, from 0.8 wt % to 1.2 wt % niobium, from 0.13 wt %to 0.17 wt % carbon, up to 0.2 wt % manganese, up to 0.015 wt %phosphorous, up to 0.10 wt % copper, up to 0.25 wt % iron, up to 0.10 wt% silicon, up to 0.04 wt % zirconium, from 0.001 wt % to 0.008 wt %boron, up to 0.005 wt % sulfur, up to 0.005 wt % nitrogen, up to 0.003wt % oxygen, up to 0.0005 wt % silver, up to 0.0005 wt % lead, up to0.00005 wt % selenium, up to 0.00003 wt % bismuth, up to 0.00005 wt %tellurium, up to 0.00005 wt % thallium, and the balance nickel andinevitable impurities.
 2. A process for repairing at least one crack ina metal workpiece comprising the steps of: forming a braze pastecontaining a first nickel base alloy material containing boron andchromium and a second nickel base alloy material containing chromium andcobalt; applying said brazing paste to an area of said metal workpiececontaining said at least one crack; subjecting said brazing paste andsaid workpiece to a brazing cycle by heating said brazing paste and saidworkpiece; and wherein said braze paste forming step comprises mixing afirst nickel base alloy material consisting from 14 wt % to 16 wt %chromium, from 2.4 wt % to 3.0 wt % boron, up to 0.15 wt % total otherelements, and the remainder nickel and inevitable impurities and asecond nickel base alloy material consisting of from 22 wt % to 23 wt %chromium, from 18.5 wt % to 19.5 wt % cobalt, from 3.5 to 4.0 wt %titanium, from 1.8 wt % to 2.2 wt % tungsten, from 1.7 wt % to 2.0 wt %aluminum, from 1.2 wt % to 1.5 wt % tantalum, from 0.8 wt % to 1.2 wt %niobium, from 0.13 wt % to 0.17 wt % carbon, and the balance nickel andinevitable impurities.
 3. A process according to claim 2, wherein saidheating step comprises heating said brazing paste and said workpiece toa temperature in the range of 2000 degrees Fahrenheit to 2200 degreesFahrenheit.
 4. A process according to claim 2, wherein said braze pasteforming step providing said first and second nickel base alloy materialsin powder form and mechanically mixing said first and second nickel basealloy materials.
 5. A process according to claim 2, further comprisingprefilling said at least one crack with said second nickel base alloymaterial.
 6. A process according to claim 2, wherein said braze pasteforming step comprises forming a paste containing from 20 wt % to 60 wt% of the first nickel base alloy material and the balance comprisingsaid second nickel base alloy material.
 7. A process according to claim6, wherein said braze paste forming step comprises forming a braze pastewith a 1:1 ratio of said first nickel base alloy material to said secondnickel base alloy material.
 8. A process according to claim 1, whereinsaid braze paste forming step providing said first and second nickelbase alloy materials in powder form and mechanically mixing said firstand second nickel base alloy materials.
 9. A process according to claim1, further comprising prefilling said at least one crack in said turbineengine component with said second nickel base alloy material.
 10. Aprocess according to claim 1, wherein said braze paste forming stepcomprises forming a paste containing from 20 wt % to 60 wt % of thefirst nickel base alloy material and the balance comprising said secondnickel base alloy material.
 11. A process according to claim 1, whereinsaid braze paste forming step comprises forming a braze paste with a 1:1ratio of said first nickel base alloy material to said second nickelbase alloy material.